The invention relates to a pyrotechnic mixture for producing a smoke screen.
Such mixtures are known per se. Hygroscopic compounds, such as metal chlorides (ZnCl.sub.2, FeCl.sub.3, AlCl.sub.3, TiCl.sub.4, SiCl.sub.4) or phosphorus oxides (P.sub.2 O.sub.3, P.sub.2 O.sub.5) are produced, evaporated and then hydrolyze with air to form smoke clouds suitable for camouflage. Regarding the mechanism of this method of smoke generation see H. Ellern, Military and Civilian Pyrotechnics, Chem. Publ. Comp., Inc., N.Y., 1968, pages 147-151; John A. Conkling, Chemistry of Pyrotechnics, Marcel Dekker Inc., N.Y., 1985, pages 174, 175.
Due to hydrolysis with humid air, the resulting smoke, particularly a smoke composed of hexachloroethane containing, so-called HC smoke, compositions, but also phosphorus smoke compositions, is highly acidic since it is primarily hydrochloric acid (HC smoke) or phosphorus acids (phosphorus smoke) that are formed. The smoke is therefore toxic and incompatible with plant life.
Moreover, in the smoke mixture most frequently employed which is based on hexachlorethane (HC) and zinc or zinc oxide, the heavy metal zinc is discharged into the environment.
There has been no lack of attempts to overcome these drawbacks. For example, the pyrotechnic smoke compositions disclosed in German Patents Nos. DE-PS 2,743,363 and DE-AS No. 2,819,850 are constructed in such a manner that the acid effect of the resulting smoke is partially or completely cancelled out by corresponding chemical complex formation or neutralization of the resulting ZnCl.sub.2 or of the phosphorus acids. However, toxic substances that are not compatible with the environment are still generated.